Browsing by Subject "Freshwater"
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Item A Collaborative Approach to Research: Balancing Freshwater Needs in a Changing Environment(2013-10-11) Mission-Aransas National Estuarine Research ReserveItem Maui's freshwater : status, allocation, and management for sustainability(2010-08) Grubert, Emily; Webber, Michael E., 1971-; Pierce, Suzanne; Jablonowski, ChristopherThe water system on Maui Island in Hawaii is an integral part of the island’s infrastructure, affecting energy, agriculture, waste, and domestic systems. Both the built and the natural water systems are likely to be altered over the coming decades. Maui’s two major industries are agriculture and tourism, which compete for water and land resources. Maui faces high costs for food and fuel it must import, and agricultural efforts might shift from plantation-scale monocropping to energy production or diversified agriculture for food. Simultaneously, land use changes (like deforestation), climate change, and cyclical droughts affect Maui’s freshwater supply. Water planning and management based on careful assessment can be valuable tools for a community expecting that water will become increasingly scarce. Since water plays a large role in many other systems, choices about water allocation and use can help the island move toward solutions of multiple problems at once, including energy scarcity, coastal protection, and financial health. This work provides a dynamic snapshot of Maui’s current built and natural water systems, then analyzes two potential water management actions: pumped storage hydroelectric facilities built on existing reservoirs and use of secondary treated wastewater to irrigate biomass for power. Based on cost estimates and alternative solutions, neither of these applications are currently judged viable.Item Phylogeny and evolutionary ecology of thalassiosiroid diatoms(2006-08) Alverson, Andrew James; Theriot, Edward C. (Edward Claiborne), 1953-Salinity is a significant barrier to the distribution of diatoms, and though it is generally understood that diatoms are ancestrally marine, the number of times diatoms independently colonized fresh waters and the adaptations that facilitated these colonizations remain outstanding questions in diatom evolution. Resolving the exact number of freshwater colonizations will require large-scale phylogenetic reconstruction with dense sampling of marine and freshwater taxa. A more tractable approach to understanding the marine--freshwater barrier is to study a group of diatoms with high diversity in each habitat. The "centric" diatom order Thalassiosirales affords an excellent opportunity to study the origin and evolution of diatoms in fresh waters. Thalassiosirales is a well-supported monophyletic group common in marine, brackish, and freshwater habitats. Thalassiosirales species historically are classified into the marine Thalassiosiraceae or freshwater Stephanodiscaceae, reflecting the more generally held hypothesis that diatoms are naturally split along marine--freshwater lines. The fossil record suggests that Stephanodiscaceae traces to a single colonization of freshwater in the mid-Miocene, and in addition, Stephanodiscaceae species share a suite of complex cell wall characters, which has been interpreted as corroborating evidence for their monophyly. I reconstructed the phylogeny of Thalassiosirales and used the phylogeny to test these and other hypotheses and to address a number of other problems related to the marine--freshwater boundary in diatoms. Phylogenetic analyses showed strong evidence for multiple colonizations of freshwater and reject all previous colonization hypotheses. Results further show that part of Stephanodiscaceae is an early diverging lineage within Thalassiosirales, indicating that these two distantly related and separately derived Stephanodiscaceae lineages independently evolved a similar set of complex morphological features upon or shortly after the colonization of fresh waters. Finally, marine and freshwater diatoms, including Thalassiosirales, show several important differences in silicon physiology. In addition to containing an order of magnitude more silica in their cell walls, freshwater diatoms have a drastically lower enzymatic affinity for silicic acid, the dissolved form of silica used by diatoms. I sequenced the silicon transporter genes from marine and freshwater Thalassiosirales and show that physiological differences are not due to differences in the coding sequence.Item The uncertain future of global freshwater resources(2015-05) Ferré, Megan Dunleavy; Johnson, Joel P.; Mohrig, David; Pierce, SuzanneProjections regarding the future of conditions on Earth vary widely. Climate change, both human-induced and naturally-forced, is expected to have many far-reaching implications, including altering current global weather patterns and terrestrial freshwater supply. Already, terrestrial water fluxes have been affected by human demand and interventions. Examples of human-induced impacts include dam and reservoir building, water withdrawals from ground and surface water for agricultural, industrial, and municipal use, as well as environmental sanitation impacts. Since the 1970's, concurrent with rising global mean temperature, freshwater discharge from rivers to the world's oceans has been decreasing. In the United States, the Southwest (from the headwaters of the westernmost Colorado River to the Mexican border, encompassing California, Nevada, Utah, and Colorado) has experienced three extreme drought years since the start of the 21st century. Projections indicate that precipitation over the lower mid-latitude continental regions, including the southwestern United States, will continue to decrease as a result of continuing greenhouse gas emissions and increasing global mean temperature. Colorado River flow reached the ocean in mid-2014 as part of a restorative experiment agreed to by the United States and Mexico, but had not previously reached the ocean since 1998. Rivers in Australia, Africa, and Asia are experiencing the same phenomena, with human extraction impairing the river’s natural ability to meet the sea. There are political and technological techniques that could mediate regional decreases in freshwater supply. In particular, large changes in agricultural use are necessary to compensate for oncoming climate shifts and to ensure that the worldwide population has access to enough water for survival.Item Where the river meets the sea : an initial investigation into the Riverine tidal freshwater zone(2017-12) Jones, Allan Edward; Cardenas, Meinhard Bayani; Moffett, Kevan B; Johnson, Joel P; Rempe, Daniella M; McClelland, James W; Hodges, Ben RRiverine tidal freshwater zones (RTFZs) are transitional environments between terrestrial and coastal waters that have freshwater chemistry and tidal physics, and are neither river nor estuary. The residence time dynamics of RTFZs have not yet been discussed in the literature, but may ultimately control the timing and magnitude of freshwater and nutrient coastal discharges. Furthermore, climate change threatens to alter the nexus between the terrestrial hydrologic cycle and the coastal tidal environment where the RTFZ resides. This dissertation provides the foundation for investigations into RTFZs and their subsequent residence times. An initial residence time analysis of 15 tidal river reaches along the south Texas Gulf Coast introduces tidal river reaches into the lentic/lotic nomenclature. This residence time analysis also quantifies the vernacular of lentic (reservoir-like) and lotic (riverine) systems via the Freshwater Continuum Classification (FCC). The FCC framework also incorporates temporal hydrologic variability, which is typically absent from other lentic/lotic classifications. Further analysis on one of these systems (Aransas River, TX, USA) revealed an RTFZ. The analysis empirically observed RTFZ responses to precipitation and tide, while providing the RTFZ definition. The RTFZ is defined by three longitudinal points of interest: λ₁ – upstream limit of brackish water, downstream limit of freshwater, and downstream boundary of RTFZ; λ₂ – upstream limit of bidirectional tidal velocities; λ₃ – upstream limit of tidal stage fluctuations and of the RTFZ. The RTFZ was typically (median) 59.9 km long and typically (median) began 11.84 km upstream (15.43 km/11.16 km, max/min) of the river mouth. From field data collected during RTFZ isolation, a tidal rating curve was created to model tidal discharge. The tidal rating curve expanded on traditional non-tidal gauging methods by incorporating stage-rate-of-change observations into the typical stage to discharge relationship. The method was performed on several sites along the Mission and Aransas Rivers, TX, USA, and twelve USGS tidal gauging stations, and resulted in strong agreement between estimated and observed discharge (i.e., r² > 0.70). With the tidal discharge estimations and RTFZ observations, future investigations should focus on RTFZ residence times and their impacts on estuarine ecology.